This invention relates to the field of percussive tools used in drilling. More particularly, the invention relates to the field of downhole hammers which are actuated by the pressure of the drilling fluid. Some of these tools are generally known in the petroleum drilling industry simply as “downhole mud hammers”.
Typically, downhole hammers are used to affect periodic mechanical impacts upon a drill bit. Through this percussion, the drill string is able to more effectively apply drilling power to the formation, thus aiding penetration into the formation.
The prior art has addressed the operation of a downhole hammer actuated by drilling mud. Such issues have been addressed in the U.S. Pat. No. 5,396,965 to Hall, which is herein incorporated by reference for all that it contains. The '965 patent discloses improvements in downhole mud actuated hammers. According to its broadest aspect the invention is a downhole mud actuated hammer for use in a drill string, which includes a housing with an upper end having means for connecting to the drill string. A throat is located within the housing which throat includes a main flow passage to allow high pressure drilling mud to pass therethrough. A piston is provided which is adapted to move axially within the housing means to thereby reciprocate between an up position and a down position. The piston is moved between the up and down position by a minor portion of the high pressure mud which portion passes from the main flow passage into at least one piston actuating chamber. This minor portion of mud is exhausted from the piston actuating chamber to a low pressure region out of the housing without being returned to the main flow passage.
U.S. Pat. No. 6,367,565 to Hall, which is also herein incorporated by reference for all that it contains, discloses a method of creating an electric signal that describes the motion of a downhole, fluid-driven percussive tool. The signal is obtained by attaching an electromagnetic transducer to the percussive tool, the member impacted by it, or the drill string. The rebound characteristics of the tool yield a measurement of the physical characteristics of the subterranean formation being penetrated. The tool's position over time is useful for diagnosing and regulating the operation of the tool. The transducer can also be configured to generate a signal large enough to be used as a power source.